Television receiving connection



1940- K. SCHLESINGER TELEVISIdN RECEIVING CONNECTIGN Filed Nov 20, 1935 g9 quencies, including the D. C. components, and the transformer I2. If a variable bias of this '20 Patented Dec. 24, 1940 UNITED STATES PATENT OFFICE TELEVISION RECEIVING GONNECTION Kurt Schlesinger, Berlin, Germany, assignor, by mesne assignments, to Loewe Radio, Inc., a cor pcration of New York Application November 20, 1935, Serial No. 50,739 In Germany November 22, 1934 2 Claims. (Cl. 178-73) I The invention relates to television receiver viding line, which may be adjusted to any fixed circuits, more particularly to filter arrangements value by the battery H. This dividing line in to separate the synchronising impulses from the the case of a powerful signal should be image urr nt, situated in Fig. la at the level designated I3a,

o The invention relates to television receivers and in the case of a weak signal (Fig. 1b) its 5 for co-operation with a television transmitter in height should be to smaller extent above the which the carrier wave of the transmitter is rezero line, and it is designated 1%. duced to zero in the case of, and only in the Such a variation of the bias of the amplitude case of, the synchronisation signals. filter 8 in accordance with the received signal 10 In the drawing Figs. la and 1 b show a diastrength is possible by means which are known 10 gram of the intensities in the image circuit of per se, but such a method represents a consida television receiver. erable difiiculty and is accompanied by the dan- Fig. 2 shows an amplitude filter circuit conger of failure, as it may readily occur that an nected to the ultra-short wave audion stage by automatically regulated bias of this kind is too a coupling condenser. small and in consequence allows also image sig- 15 In Fig. 3 there is provided instead of the counals to pass through the glow discharge tube 8, pling condenser a D. C. coupling. in the same manner as it may also readily be If a transmission of this nature is picked up the case that the bias is too high and accordby a receiver which can accommodate all freingly does not allow any signals at all to reach if condenser couplings are not provided in the kind is to be avoided, i. e., replaced by a fixed receiver circuit, up to the cathode ray tube, a direct potential, it is apparently only possible to diagram of amplified received signals has the adopt the course of maintaining the signal appearance of Fig. in for powerful and Fig. 1b strength constant at the resistance ii. The for weak. reception. The invention relates to methods necessary for this purpose are well the amplitude filter, which has the known funcknown in the radio art as fading compensation tion of separating the synchronisation peaks 1 methods. In this case they would preferably from the image current 2. Difficulties occur in consist in the fact that the amplitude of the seppractice due to variation in the sensitivity of the arated synchronisation'signals is utilised or the receiver or variation in the strength of the re- D. C. mean value thereof as regulating potenceived signal due to fading. Fig. 2 illustrates tials. This method, however, is also very arthe reason for these diflioulties and shows the tificial and not sufficiently reliable. final rectifier of an intermediate-frequency am- The invention consists of a method differing plifier, viz., a twice grid detector whose grids are from those referred to, and is based on the idea coupled with the intermediate-frequency transthat a direct coupling is introduced between the former 3 and whose anode resistance is directly amplitude filter B and the connecting resistcoupied to the grid electrode of the Braun tube ance 4. Q. If an amplitude filter, for example a glow Fig. 3 serves for explanation. It again shows discharge tube 8, is coupled with the lead 5 the anode circuit 4 of the final detector l5, which through a condenser 1, it is possible to impart is directly coupled with the grid lead 5 of the to the cathode 9 of this tube through the leaktelevision tube 6. According to .the invention, age resistance ill a positive bias of such amount the cathode 9 of the filter tube 8 is connected that a correct separation of the synchronisation with this lead 5 directly, 1. e., not through the signals is effected for a certain definite received medium of condensers, while from a potentiomstrength of signal so that the glow discharge eter [4, which is connected in parallel to the tube 8 in the anode circuit passes to the transanode potential source 2'! of the detector l5, former I2 the synchronisation signals and noththere is conducted to the anode of the tube 8 ing more. This bias ll, however, should be via the output transformer or transformers [2, I2 varied continuously in accordance with the varia bias of such extent that a stream of elecation in the strength of the signals, and the trons is able to flow through the tube 8 only use of a condenser 1 means that the glow diswhen the carrier wave completely ceases, i. e., charge tube is excited by alternating potentials, upon maximum current value of the detector which rise and fall in proportion to the strength and in a very small potential range above the of the received signals. An amplitude filter of value zero of the carrier. As well known, the this nature marks in effect in Figs. 1a, 1b a didetector as shown has the property of providing a maximum current when the reception ceases. In the curves in Fig. 1 the new threshold which remains constant independently of the strength of the reception is shown in broken lines in both figures at the same level and designated M. It Will be clearly recognisable that only the shaded potential values which are situated between this level I4 and the zero line in the reception diagram are capable of being passed through the filter tube 8, immaterial of the strength to which the reception is otherwise adjusted. The filter circuit accordingly deals only with the maxima of the synchronisation signals, and separates a constant potential range proceeding from the maximum, whilst in known connections the line of separation was disposed at the bounding line between image and synchronisation signals and in consequence the filter signals were of greatly varying amplitude and moreover difficulties were encountered in obtaining a clean limited curve between image and synchronisation signals. An

additional advantage of the new method consists in the fact that the position of the zero line at which the reception disappears is completely independent of the adjustment of any amplifying tubes of the receiver, and is only dependent on the biases of the final rectifier, with which the filter tube is directly coupled. According to the invention, there are selected output detector circuits which operate with zero grid bias, which is the case for example for that shown in the drawing, as connections of this detector ofier the greatest guarantee that the adjusted level will not again vary in the course of time. Furthermore, according to the invention, the potentiometer I4 is made to be operable from the outside of the apparatus, in order to be able to adjust the strength of the synchronisation signal once and for all to the optimum amount which acts reliably on the relaxation apparatus but does not overload the same. The fact that the separated peaks of the synchronisation signals do not contain a remainder of carrier frequency, as no further carrier frequency is transmitted, facilitates accurate synchronisation and represents an additional advantage as compared with methods which make use of separating lines such as I311, I31).

By reason of the direct coupling with the filter according to the invention the independence of the synchronisation from the intensity of the received signal is definitely solved. The adjustment of the intensity of the received signal may accordingly take place independently thereof by special means. It is even proposed according to the invention to regulate the amplitude of the signal output by means of a circuit or a special diode which has no further connection with the synchronisation circuit illustrated in Fig. 3, and in particular is not capable of interfering with the bias 14.

I claim:

1. In a television receiving system wherein picture and synchronizing signals are received as a modulation of a common carrier and wherein the carrier amplitude reaches a substantially fixed predetermined level for the synchronizing signals comprising a detector having a cathode, a control electrode and an output electrode, means for applying the picture and synchronizing signals to be detected between the control electrode and the cathode of said detector, means includ ing an impedance for maintaining the detector output electrode positive with respect to the cathode, a synchronizing signal separator tube including a cathode and an output electrode, means for directly connecting the cathode of the separator tube to the output electrode of the detector tube, and means for normally maintaining the output electrode of the separator tube negative with respect to its associated cathode by a voltage difference of such magnitude that current will be passed by the separator tube only during the intervals that synchronizing signals are received whereby all synchronizing signals in excess of a substantially constant predetermined amplitude are separated from the picture signals irrespective of the strength of the picture signals.

2. In a television receiving system wherein picture and synchronizing signals are received as a modulation of a common carrier and wherein the carrier amplitude reaches a substantially fixed predetermined level for the synchronizing signals and wherein said synchronizing signals are of a predetermined duration following each train of picture signals for each scanned line and of a different predetermined duration following successive trains of picture and line synchronizing signals to represent each scanned picture field comprising a detector having a cathode, a control electrode and an output electrode, means for applying the picture and synchronizing signals to be detected between the control electrode and the cathode of said detector, means including an impedance for maintaining the detector output electrode positive with respect to the cathode, a synchronizing signal separator tube including a cathode and an output electrode, means for directly connecting the cathode of the separator tube to the output electrode of the detector tube, and means for normally maintaining the output electrode of the separator tube negative with respect to its associated cathode by a voltage difference of such magnitude that current will be passed by the separator tube only during the intervals that synchronizing signals are received whereby all synchronizing signals in excess of a substantially constant predetermined amplitude are separated from the picture signals irrespective of the strength of the picture signals.

KURT SCI-ILESINGER. 

